Analog television broadcasts are becoming changed to digital television broadcasts. So far, digital satellite broadcast services using CS (Communication Satellites) have been started. In addition, digital satellite broadcast services using BS (Broadcasting Satellites) are being prepared. Moreover, digital television broadcasts using ground waves are scheduled to be started.
In digital television broadcasts, since the frequency efficiency is improved, more channels can be assigned than analog television broadcasts. In addition, HDTV (High Definition Television) broadcasts can be easily performed. Moreover, in digital television broadcasts, various services such as bi-directional service, data delivery service, and video-on-demand that are not available in conventional analog television broadcasts can be accomplished.
A television receiver that receives such a digital television broadcast is conventionally structured as shown in FIG. 1.
In FIG. 1, a received signal is supplied from an input terminal 101 to a tuner circuit 102. In the case of a CS digital broadcast, a signal of 12 GHz band is received by a parabola antenna (not shown). The received signal is converted into a signal of 1 GHz band by a low noise converter disposed in the parabola antenna. The converted signal is supplied to the tuner circuit 102. The tuner circuit 102 selects a carrier frequency signal of a desired channel from the received signal and performs a demodulating process and an error correcting process for the selected signal. As a result, the tuner circuit 102 decodes the selected signal to a transport stream composed of video packets and audio packets.
An output of the tuner circuit 102 is supplied to a demultiplexer 103. The demultiplexer 103 separates the transport stream into video packets and audio packets.
The video packets are supplied to a video decoder 104. The audio packets are supplied to an audio decoder 105. The video decoder 104 performs a decompressing process for the video packets corresponding to for example the MPEG 2 (Moving Picture Experts Group) system so as to decode the video packets to video data. In addition, the audio decoder 105 performs a decompressing process for the audio packets corresponding to the MPEG system so as to decode the audio packets to audio data.
The video data decoded by the video decoder 104 is supplied to a graphics processing circuit 106. The graphics processing circuit 106 performs a picture process. An output of the graphics processing circuit 106 is output from an output terminal 107. An output of the audio decoder 105 is output from an output terminal 108.
The tuner circuit 102, the demultiplexer 103, the video decoder 104, the audio decoder 105, and the graphics processing circuit 106 are controlled by an MPU (Micro Processor Unit) 111. A bus 111 extends from the MPU 111. The tuner circuit 102, the demultiplexer 103, the video decoder 104, the audio decoder 105, and the graphics processing circuit 106 are connected to the bus 110.
In addition, a modem 112 and for example an IEEE (Institute of Electrical and Electronics Engineers) 1394 interface 113 are connected to the bus 110. The modem 112 is used to perform a charging process. The IEEE 1394 interface 113 exchanges a stream with an external device.
As was described above, in a conventional receiver for a digital television broadcast, the entire receiver is controlled by an MPU. The MPU centrally controls each portion of hardware using commands thereof in consideration of precise timing levels thereof.
However, in that method of which the MPU centrally controls the entire device in consideration of each portion of the hardware, since the design work should be performed for each device, if the design of the device is changed, software should be largely rewritten and hardware should be largely changed. Thus, the developing efficiency of such a method is low. In addition, since parts cannot be used in common or structured as modules, the cost of the device may rise. In addition, the size of the device may become large. Moreover, digital television broadcasts provide various types of services. Thus, in the method of which the MPU centrally manages the entire device, it is difficult to deal with new services.
To solve such a problem, functions necessary for a television receiver may be structured as blocks and connected through a common bus. When such a bus is used, the design efficiency of the device can be improved and the design change thereof can be easily performed.
In addition, when a bus is standardized, by adding hardware for providing an extension function to the bus, a new service can be used. For example, when an extension plug-in card for an extension function is prepared and connected to the bus through an interface, various functions and services may be newly added.
However, when hardware for an extension function is connected to the bus, to cause the hardware to operate, the host MPU should recognize the hardware and issue commands to the hardware. To allow the host MPU to issue commands to the hardware, software may have to be installed to the host MPU. The install work for the software may be troublesome for non-experienced users of television receivers.
Therefore, an object of the present invention is to provide a digital signal processing apparatus, a system thereof, and an extension function providing method that allow hardware for an extended function to be easily connected to a bus for a device of which required functions are structured as blocks and connected through a standardized bus.